further to the point of when did the arabs start marrying their fathers’ brothers’ daughters (fbd marriage), from kudelin (2005) – “Family-Matrimonal Relations in the 5th-7th Centuries Arabia and Their Reflection in the Early Arabic Poetry” [pgs. 8-9]:

“According to one point of view, in the 5th-7th century Arabia there was a decay of the communal-clan system which was reflected, in particular, in the ‘tendency towards isolation of a consanguine group by regulating family and matrimonial relations’ with the transformation of such group from an exogamic into an endogamous one. At that period the exogamic form of marriage was gradually losing its ‘oneness and ubiquity’ and edogamy was becoming firmly established. Obviously, during some period of time both forms of marriage coexisted simultaneously….

“Consistent introduction of paternal relations and the distribution of endogamy lead to such well-known form of matrimonial relations as [fbd] marriage which prevailed on the Arabic Peninsula from the 6th-7th century. In the conditions of the growing role of endogamy in this period the most suitable spouses in the Arabic society were ‘a son of an uncle on the father’s side’ (*ibn ‘amm*) and ‘a daughter of an uncle on the father’s side (*bint ‘amm*). If a girl did not have a first cousin, the right to marry her passed to the patrilineal cousins of further degrees. Usually the right did not pass further than the girl’s cousins of the third or fourth degrees…. In case of divorce, the right for the woman passed to other patrilineal cousins, beginning from the closest degree of kinship. An agnatic cousin had the right not to marry his relative, while she could not marry anyone else without his consent. An exterior competitor had to ask a patrilineal cousin for his permission and even pay him ‘compensation’….

“The coexistence of the exogamic and the endogamous forms of marriage in the 5th-7th century Arabia was reflected in the early Arabic poetry and determined its uniqueness.”

so it looks as though that, thanks to a quirky twist of history (the fall of the roman empire, perhaps?), the arabs adopted the form of cousin marriage that leads to the most inbreeding (fbd marriage) at just around the same time that europeans (especially northwest europeans) began to abandon cousin marriage altogether. how’s THAT for a clash of civilizations?!

around three or four hundred years after europeans started taking the medieval church’s cousin marriage bans seriously (ca. the 800s judging by the franks — ymmv), european languages shifted to reflect this change in mating patterns. a general term for “cousins” (and aunts and uncles) became the norm, replacing the older terms which specified “mother’s brother’s daughter” or whatever. it was no longer necessary to distinguish the “bint ‘amm” (father’s brother’s daughter in arabic) or “biǎo” cousins (cousins other than those descended from the father’s brother in chinese [mandarin?]) because all cousins were now off limits as far as marriage was concerned. this linguistic shift occurred between the twelfth and fifteenth centuries in german and also happened in english, french, etc. (interestingly, a similar linguistic shift happened in ancient greek, indicating…?)

the funny thing is, though, that the same linguistic shift also happened in italian, even though plenty of (especially southern) italians kept right on marrying their cousins — up until, like, yesterday. well, now i’ve stumbled across some historic regional differences in kinship terminology in italy. from “Land, Kinship, and Consanguineous Marriage in Italy From the Seventeenth To the Nineteenth Centuries” [pgs. 532-533]:

“In a rural town of Calabria in the province of Catanzaro, patrilateral parallel cousins were called *cugini giusti* (right cousins), or *surrea* and *frateu* in the case of the patrilateral parallel female and male cousins, respectively….

“At Prodo, in Umbria, we find virtually the same terminology as in Calabria. The strongest bond was between the males; patrilateral parallel cousins were called ‘brother-cousins,’ while others were simply called cousins….

“In Desulo, first cousins through brothers were known as *karrales*, and even second cousins, the sons of *karrales*, were referred to as *ermanos primargios*.”

so there you go. and there’s only something on the order of a million and one dialects in italy, so who knows how many different terms there might be for cousins in “italian” (and how those terms might differ regionally)?
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from anglo-saxon england, from the laws of wulfstan (d.1023), apparently the punishment (or one of the punishments) for violating the incest laws was a fine — a fine reckoned based upon how closely you were related to your partner in crime. sounds like it was a bit like applying some sort of wergeld calculation in order to try to enforce the cousin marriage bans. never heard this before [pg. 227]:

“There is particular concern and precision in the laws associated with Wulfstan: ‘if anyone commits incest, he is to pay compensation according to the degree of relationship, whether by wergeld or by fine or by all his possessions. It is not equal whether a man has intercourse with his sister, or with a more distant relation.’ Laws composed by Wulfstan prohibited marriage ‘within the sixth degree of relationship, that is within the fourth knee [*cneowe*]’, thus prohibiting marriage to fourth cousins, or marriage ‘with the widow of a man as nearly related to him as this’.”